The University of Southampton nanomechanical fibers were fabricated with two light-carrying cores suspended less than 1 µm apart. The cores are close enough to each other to be optically coupled.

A demonstration of the structure of the dual-core nanomechanical optical fiber developed at the University of Southampton. Inside the fiber, two cores are shown suspended from above and below. This innovative structure enables the two cores to move and precisely respond to an external mechanical force, moving closer or farther apart, depending on data transmission needs. Images courtesy of Optics Express.
“Nanomechanical optical fibers do not just transmit light like previous optical fibers,” said Wei H. Loh, deputy director of the EPSRC Centre for Innovative Manufacturing in Photonics and researcher at the Optoelectronics Research Centre, both at the University of Southampton. “Their internal core structure is designed to be dynamic and capable of precise mechanical motion. This mechanical motion, created by applying a tiny bit of pressure, can harness some of the fundamental properties of light to give the fiber new functions and capabilities.”

Shifting the position of one of the cores by just a few nanometers changed how strongly the light responded to this coupling effect, the researchers said. If the coupling effect is strong enough, the light immediately jumps from one fiber to the other.

“Think of having a train traveling down a two-track tunnel and jumping the tracks and continuing along its way at the same speed,” Loh said. The flexible suspension system of the fiber easily responds to the slightest bit of pressure, bringing the two cores closer together or moving them apart, thereby controlling when and how the signals hop from one core to the other, reproducing the function of an optical switch inside the actual fiber.

This same capability could also enable difficult-to-achieve optical buffering.

“With our nanomechanical fiber structure, we can control the propagation time of light through the fiber by moving the two cores closer together, thereby delaying or buffering the data as light,” Loh said. Buffers are essential when multiple data streams arrive at a router at the same time; they delay one data stream so another can travel freely.

The new fibers were created by heating and stretching a specifically shaped tube of optical glass with a hollow center that contained two cores suspended from the inside wall. This original structure is maintained when the fibers are drawn and stretched to the desired thickness.

An actual cross section and extreme magnification of the nanomechanical fiber. The dual cores are shown in the center, each a mere 0.5 µm across at its center, while the supporting glass filament is approximately 0.2 µm across. The small-scale structure was achieved by heating and drawing out a larger fiber optic form.
This is the first time that nanomechanical dual-core fibers have been directly fabricated, the researchers said. Other types of multicore fibers have been fabricated, but their cores are encased in glass and mechanically locked. Such designs meant that routing, switching and buffering data required taking the light out of the optical fiber for processing in the electronic domain before reinsertion back into the fiber, which is cumbersome and costly.

The new process utilizes traditional fiber optic manufacturing methods, making it possible to create dual-core fibers that are hundreds of meters to several kilometers long — a necessity for telecommunications.

Loh and his colleagues expect this introduction of microelectromechanical systems (MEMS) functionality into the optical fiber to have implications in other fields, such as sensing.

“Nanomechanical fibers could one day take the place of silicon-based MEMS chips, which are used in automobile sensors, video game controllers, projection displays and other everyday applications,” Loh said. Because the fibers are so sensitive to pressure and can be readily drawn to long lengths, they also could be integrated into bridges, dams and other buildings to signal subtle changes that could indicate structural damage.

Next, the fibers will be tested at longer lengths, and enhancements will be made to the precision with which they perform switching and other functions. Such fibers could begin to optimize telecommunications and industrial systems within the next three to five years, the scientists said.

The research, to be presented in March at OFC/NFOEC 2013 in Anaheim, Calif., was reported in Optics Express.